So-called blister packages are formed from a foil of thermoplastic material, e.g. polyvinylchloride, initially provided with a multiplicity of generally cup-shaped depressions or blisters designed to receive pills or similar articles to be stored. The preformed foil is heat-sealed onto a carrier strip, usually of metal, from which individual packages are subsequently stamped in a die-cutting operation. The packages can then be stacked for assembly in larger containers.
In commonly owned German published specification No. 27 05 293 there has been disclosed a device for stamping such packages from a continuous composite strip consisting of a preformed thermoplastic foil bonded onto an overlying metallic cover layer. The strip is advanced intermittently along a stationary support having a cutout whose outline substantially corresponds to that of the packages to be stamped. After every advance, over a distance corresponding to the dimension of the package in the transport direction, a cutting die having an outline in the shape of a rectangle with rounded corners severs a portion of the strip whose lateral edges project slightly beyond those of the cutout. The severed strip portion, constituting a sealed package, enters the cutout for assembly into a stack of such packages whereupon the die is retracted and the transport mechanism takes another step.
In the ideal case, in which the pitch of the feed means--i.e. the advance of the strip between die-cutting strokes--exactly equals the width of the die in the transport direction, the leading edge of the die registers precisely with the end of the previous cut so that the newly stamped plate has a front edge merging smoothly into its rounded corners. In practice, however, such a precise coincidence is difficult to achieve with any degree of constancy. If the advance of the strip falls short of the width of the die, its leading edge intersects the previously shaped strip boundary in the region of the corners where that boundary has an opposite curvature; as a result, unsightly and potentially dangerous pointed projections are formed near the corners of the front edge of the newly stamped plate. If, on the other hand, the advance exceeds the width of the die, a transverse web of greater or lesser thickness remains wastefully connected with the stamped-out strip.